This invention relates generally to bullets, and more particularly to small caliber bullets having a metal jacket and a hollow point.
Bullets are jacketed to improve the ability of the bullet to penetrate barriers and remain intact. Most commonly the jacket (typically copper) is plated onto the core (typically lead). This results in a thin, uniform jacket that provides more structural integrity to the bullet and improves penetration in at least some circumstances.
Another type of jacketed bullet is made by forming a cup-shaped jacket perform (typically copper) and inserting a preformed core (typically lead) into the jacket perform, bonding the core to the jacket, and forming the open front end of the jacket into the front end of the bullet, so that the thickness of the jacket increases toward the back of the bullet.
Another type of jacketed bullet is made by forming a cup-shaped jacket preform (typically copper) and inserting a preformed core (typically lead) into the jacket preform and swaging the core and jacket together, and forming the closed end of the bullet into the front of the bullet. This type of jacketed bullet is more completely described in co-assigned U.S. Pat. No. 5,208,424, the entire disclosure of which is incorporated by reference. While the thickness of the jacket of this bullet tapers toward the rear, the core is merely mechanically held in the jacket.
One measure of bullet performance is the Federal Bureau of Investigation Ammunition Test Protocol. This Protocol is a series of tests that measure a bullet's ability to defeat different types of barriers, penetrate the target, and retain mass and expand to cause maximum damage to the target. The Protocol assesses a bullet's ability to inflict effective wounds after defeating various intervening obstacles commonly present in law enforcement shootings. The overall results of a test are thus indicative of that specific cartridge's suitability for the wide range of conditions in which law enforcement officers engage in shootings.
According to the FBI Ammunition Test Protocol, bullets are fired into 6×6×16 inch blocks of 10% Ballistic Gelatin (Kind & Knox 250-A) at 4° C. (39.2° F.) five times in eight separate events. Each shot's penetration is measured to the nearest 0.25 inch. The bullet is recovered, weighed, and measured for expansion by averaging its greatest diameter with its smallest diameter. The test events are:
Test Event 1: Bare Gelatin The gelatin block is bare, and shot at a range of ten feet measured from the muzzle to the front of the block.
Test Event 2: Heavy Clothing The gelatin block is covered with four layers of clothing: one layer of cotton T-shirt material (48 threads per inch); one layer of cotton shirt material (80 threads per inch); a one layer of Malden Mills Polartec 200 fleece; and one layer of 14.4. ounces per yard cotton denim (50 threads per inch). The block is shot at ten feet, measured from the muzzle to the front of the block.
Test Event 3: Steel Two pieces of 20 gauge, hot rolled steel with a galvanized finish are set three inches apart. The gelatin block is covered with Light Clothing and placed 18 inches behind the rear most piece of steel. The shot is made at a distance of 10 feet measured from the muzzle to the front of the first piece of steel. Light Clothing is one layer of the above described T-shirt material and one layer of the above described cotton shirt material.
Test Event 4: Wallboard Two pieces of half-inch standard gypsum board are set 3.5 inches apart. The pieces are six inches square. The gelatin block is covered with Light Clothing (as described in Test Event 3) and placed 18 inches behind the rear most piece of gypsum. The shot is made at a distance of ten feet, measured from the muzzle to the front of the first piece of gypsum.
Test Event 5: Plywood One piece of three-quarter inch AA fir plywood is used. The piece is six inches square. The gelatin block is covered with Light Clothing (as described in Test Event 3) and placed 18 inches behind the rear surface of the plywood. The shot is made at a distance of ten feet, measured from the muzzle to the front surface of the plywood.
Test Event 6: Automobile Glass One piece of A.S.I. one-quarter inch laminated automobile safety glass measuring 15×18 inches is set at an angle of 45° to the horizontal. The line of bore of the weapon is offset 15° to the side, resulting in a compound angle of impact for the bullet upon the glass. The gelatin block is covered with Light Clothing (as described in Test Event 3) and placed 18 inches behind the glass. The shot is made at a distance of ten feet, measured from the muzzle to the center of the glass pane.
Test Event 7: Heavy Clothing at 20 yards. This event repeats Test Event 2 but at a range of 20 yards, measured from the muzzle to the front of the gelatin.
Test Event 8: Automobile Glass at 20 yards. This event repeats Test Event 6 but at a range of 20 yards, measured from the muzzle to the front of the glass, and without the 15° offset.
A composite score of the 40 shots is then established, with the maximum score being 500. A higher score generally indicates a more consistent performing bullet under wide ranging conditions. The parameter that has the highest impact on overall score is the standard deviation of penetration amongst all 40 shots. If even a single shot fails to upset, it will subsequently over penetrate and increase the measured standard deviation thus resulting in a lower score. Existing jacketed bullets generally perform satisfactorily on the FBI Ammunition Test Protocol, with scores ranging from 275 to 375 for plated jacketed bullets, and from 200 to 325 for bullets made with jacket preforms. While functional, there was clearly room for improvement, at least as measured by the FBI Ammunition Test Protocol.